1. Field of the Invention
This invention relates generally to array type antennas for transmitting and receiving RF energy at UHF frequencies, and more particularly to a hexagonal array antenna for limited scan spatial applications with triangular grid and overlapped sub-apertures.
2. Description of Related Art
There is a need for an antenna for a Mobile User""s Objective System (MUOS) which is a spatial communication system featuring transmit and receive antenna operation at frequencies in the UHF portion of the RF spectrum. Typically this type of requirement is fulfilled with a multi-beam offset parabolic reflector. The reflector has a mesh surface and is deployed in space. Such antennas are typically 9.6 and 11.4 meters in diameter and produce 7-7.2xc2x0 beamwidth beams in a concentric formation. The problem associated with such apparatus is to produce a deployable system having limited scan but one that can be steered. Such antennas normally have many controls that make this difficult.
Accordingly, it is an object of the present invention to provide an improvement in a phased array antenna.
It is another object of the invention to provide a phased array antenna which can be deployed in space and steered over a limited field of view.
It is yet another object of the invention to provide a deployable phased array antenna system which provides scan control with an improved circuit configuration with a minimal number of controlled feed points.
The foregoing and other objects are achieved by a phased array in the form of a triangular grid of steerable antenna elements arranged in a plurality of concentric rings and which include a plurality of digital beam forming input/output ports which are substantially less in number than the total number of antenna elements, wherein each port comprises a feed point for a respective set of mutually adjacent antenna elements including a center element and a plurality of elements which surround and form a concentric ring around the center element so as to define a plurality of sub-arrays, wherein the elements of each sub-array are selectively connected and fed from input/output ports of said plurality of input/output ports so as to provide a plurality of overlapped sub-apertures, and wherein the sub-apertures are activated and controlled to generate a respective number of overlapped beams.
In a preferred embodiment, ninety-one elements are arranged in a phased array of five concentric hexagonal rings about a center element and are connected so as to form nineteen hexagonal sub-arrays of seven dipole elements each and where every second interior element is coincident with a digital beam forming input/output port connected to seven sub-aperture feed ports. The center element of each hexagonal sub-array and the elements in the outermost hexagonal ring are fed from one sub-aperture feed port while the interior elements surrounding respective center elements are fed from one sub-aperture feed port of two adjacent input/output ports by way of a signal divider element. Moreover, the center element of a sub-aperture feed has twice the power as surrounding elements of the sub-aperture A digital beam former (DBF) is used as an input on transmit or output on receive to produce proper amplitudes and phases to steer the antenna and generate overlapping beams.
Further scope of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood, however, that the detailed description and specific example, while disclosing the preferred embodiment of the invention, it is given by way of illustration only, since various changes and modifications coming within the spirit and scope of the invention will become apparent to those skilled in the art from the detailed description.